Heat shock protein 90 (Hsp90) is a "molecular chaperone" whose activity is essential for the folding and cellular stability of a number of mutated, chimeric or over-expressed proteins that promote the survival andproliferation of cancer cells. Examples of proteins whose activity is Hsp90-dependent include mutated p53, Brc-Abl, Raf-1, Src, and ErbB2. Inhibition of HspQO activity is a potential route to broad range anti-cancer agents. Geldanamycin, a small molecule that inhibits Hsp90 activity, is currently in clinical trials as a potential anti-cancer agent. Hsp90 does not function in isolation, but rather is part of a complex machinery that involves several other proteins and "co-chaperpnes". Two chaperones, Hsp70 and Hsp90, act sequentially on certain client proteins to generate the mature, active, form of the proteins. Hsp Organizing Protein (HOP) has independent binding sites for Hsp70 and Hsp90, and by binding these chaperones simultaneously, it functions to bring them into physical proximity. The interaction of HOP with Hsp70 and Hsp90 is very well characterized. HOP has two independent tetratricopeptide repeats (TRP). TPR1 binds specifically to the C-terminal peptide of Hsp70 and TPR2A binds specifically to the C-terminal peptide ofHsp90. We propose to develop HTP assays to identify specific inhibitors of the interaction of Hsp 90 withTPR2A. Inhibition of this interaction will prevent the Hsp70-Hsp90 dependent folding sequence, a nd thus lead to oncogene degradation. It has already been demonstrated in mammalian cells that preventing its interaction with HOP inhibits Hsp90 activity. We will develop fluorescent-based assays, in vitro and in vivo to identify small molecules that specifically disrupt the Hsp90-HOP interaction. We will follow-up potential leads by assaying their ability to reverse the oncogenic phenotype in HTP morphology assays. Promising compounds will go forward into trials in collaboration with other researchers.